1. Field of the Invention
The present invention relates to an inertial drive actuator which moves a movable body in a predetermined direction.
2. Description of the Related Art
An actuator which displaces a drive shaft in an axial direction by supplying a saw-tooth wave drive pulse to an electromechanical transducer fitted to the drive shaft, and moves a movable member that has been friction-fitted to the drive shaft in the axial direction has been known (hereinafter, such actuator will be called as an ‘impact drive actuator’ or an ‘inertial drive actuator’).
Such impact drive actuator has been disclosed in patent literature 1. FIG. 10A is a diagram showing an arrangement thereof. A vibration member 103 is inserted through holes cut through rising portions of a supporting member 101, and is disposed to be movable in an axial direction of the vibration member 103. One end of the vibration member 103 is fixed to one end of a piezoelectric element 102, and the other end of the piezoelectric element 102 is fixed to the supporting member 101.
Therefore, the vibration member 103 vibrates in the axial direction with the vibration of the piezoelectric element 102. Two holes are provided in a movable body 104 as well, and the vibration member 103 is inserted through these two holes. Furthermore, a plate spring 105 is fitted to the movable body 104 from a lower side, and a protrusion provided to the plate spring 105 is pressed against the vibration member 103. Due to pressing by the plate spring 105 in such manner, the movable body 104 and the vibration member 103 are friction-fitted mutually.
Drive waveforms for driving the impact drive actuator are shown in FIG. 10B and FIG. 10C. FIG. 10B shows a drive waveform for moving the movable body 104 toward right and FIG. 10C shows a drive waveform for moving the movable body 104 toward left. A principle of operation of the impact drive actuator will be described by using these drive waveforms. In the following description, a direction in which, the piezoelectric element 102 elongates is let to be a leftward direction, and a direction in which, the piezoelectric element 102 contracts is let to be a rightward direction.
A vertical axis V indicates voltage and a horizontal axis T indicates time. Same reference numerals are used in FIG. 10A and FIG. 10B.
In a case of moving the movable body 104 in the rightward direction, the drive waveform shown in FIG. 10B is used. The drive waveform has a portion that rises steeply and a portion that falls gently. At the portion where the drive waveform rises steeply, the piezoelectric element 102 is elongated rapidly. Here, since the vibration member 103 is fixed to the piezoelectric element 102, the vibration member 103 moves leftward rapidly with the rapid elongation of the piezoelectric element 102. At this time, as an inertia of the movable body 104 overcomes a friction-fitting force between the movable body 104 and the vibration member 103 (frictional force between the movable body 104 which is pressed by the plate spring 105, and the vibration member 103), the movable body 104 halts at that position without moving in the leftward direction.
Next, at the portion where the drive waveform falls gently, the piezoelectric element 102 contracts gradually. The vibration member 103 moves slowly in the rightward direction with the gradual contraction of the piezoelectric element 102. In this case, the inertia of the movable body 104 is incapable of overcoming the friction-fitting force between the movable body 104 and the vibration member 103. Therefore, the movable body 104 moves in the rightward direction, with the movement of the vibration member 103.
On the other hand, in a case of moving the movable body 104 in the leftward direction, the drive waveform shown in FIG. 100 is to be used. The drive waveform has a portion that rises gently and a portion that falls steeply. At the portion where the drive waveform rises gently, the piezoelectric element 102 is elongated gently. In this case, the vibration member 103 moves slowly in the leftward direction in response to the gentle elongation of the piezoelectric element 102. In this case, the inertia of the movable body is not capable of overcoming the friction-fitting force between the movable body 104 and the vibration member 103. Therefore, the movable body 104 moves in the leftward direction, with the movement of the vibration member 103.
Next, at the portion where the drive waveform rises steeply, as the inertia of the movable body 104 overcomes the friction-fitting force between the movable body 104 and the vibration member 103, as shown in FIG. 10B, the movable body 104 halts at that position without moving in the rightward direction.
By the plate spring 105 being pressed against the vibration member 103 all the time, the movable body 104 is supported by the vibration member 103 by friction. Therefore, even when the movable body 104 is at halt, that position is maintained.
In such manner, the impact drive actuator is an actuator in which, the friction-fitting and inertia between the movable body 104 and the vibration member 103 are used, and is an actuator which is capable of moving the movable body 104 by using the drive waveforms shown in FIG. 10B and FIG. 10C.